Are procalcitonin or other infection markers useful in the detection of group A streptococcal acute tonsillitis?

Background: The Centor criteria and the streptococcal rapid antigen detection test (RADT) are commonly used to differentiate sore throat patients with group A streptococci (GAS) from patients with other pathogens. We aimed to investigate if procalcitonin (PCT), C-reactive protein (CRP), white blood cell count (WBC), and absolute neutrophil count (ANC) could increase the diagnostic accuracy when added to the Centor score and RADT, or be used instead of the RADT, in the differential diagnosis.

Methods: A 6-month prospective study was carried out in a Danish general practice with 8 physicians. One hundred acute tonsillitis patients aged 15 to 40 y were included.

Results: The prevalence of GAS was 26%. The sensitivity (90%) and specificity (97%) of the RADT were high. Mean values of CRP, WBC, and ANC were significantly higher in patients with GAS compared to non-GAS patients (p < 0.001). However, the sensitivities (66-90%) and specificities (45-75%) were low. No difference in PCT levels was found (p = 0.334). CRP was the most reliable infection marker (sensitivity 90% and specificity 45%) for GAS aetiology.

Conclusions: The sensitivity, specificity, and area under the curve of the RADT were higher than those of the 4 measured infection markers in the differentiation between GAS and non-GAS acute tonsillitis patients. The infection markers did not increase the diagnostic accuracy when added to the Centor score and RADT. When RADT is not available, measurement of CRP or ANC may increase the diagnostic accuracy in the detection of GAS-positive patients.